Reduction of nitro and azo compounds.



PATENTED AUG. 11, 1908. M. BUCHNER. REDUCTION OF NITRO AND AZOCOMPOUNDS.

m APPLICATION PILED SEPT. 24. 1900.

N0 MODEL.

I v I I I I I d alkozum o s UNITED STAT S Patented. August 11, 1963.

PATENT OFFICE.

MAX BUCHNER, OF MANNHEIM, GERMANY, ASSIGNOR TO 0. F. BOEHRINGER &SOEI-INE, OF MANNHEIM-WALDHOF, BADEN, GERMANY, A FIRM.

REDUCTION OF NITRO AND AZO COMPOUNDS. 7

SPECIFICATION forming part Of Letters Patent N0. 736,204, dated August11, 1903.

Application filed September 24, 1900. Serial No. 30,967. (No specimens.)

.To all whom it may concern.-

pounds; and I do hereby declare the following to be a full, clear, andexact description of the invention, such as will enable others skilledin the art to which it appertains to make and use the same.

This invention relates. to the reduction of nitro and azo compounds, andparticularly to such reduction in connection with the employment of tinas a reducing agent, the pur- I pose ofmyinvention being to recover thetin I in a metallic state by economic methods and with a minimum ofwaste. Metallic tin can only be employed for such reductions in acommercially successful manner if the same can bedirectly recovered fromthe reducingbath, so that a comparatively small quantity of the-same canbe used over and over again in the reduction of comparatively largequantities of the starting materials. Hitherto a simple method of suchdirect recovery has,

been wanting. The chemical methods of recovering tin from the solutionsof its salts cannot be employed in the arts because too expensive, andthey are, moreover, obj ectionable for sanitary reasons. Although aconvenient method of precipitation is afforded by electrolysis, suchmethods have hitherto been confined to the laboratory in cases where itwas desired to recover quantitatively small amounts of tin, suchrecovery involving the exercise of the most developed skill of-theanalyst and a great waste of current. only method having any importancein the arts hitherto devised is the electrolytic recovery of tin fromtin scrap, which consists in employing such scrap as the anode in analkaline electrolyte, whereby the metallic tin is deposited or separatedon the cathode. Under this method, however, as well as when employingacid solutions, only low-current densities can be utilized, and aconsiderable amount of the current energy goes to waste, as abundantlyconfirmed in the literature of electrolysis.

The 1 this art. The state of facts above adverted to have hitherto beenmade the use of this very valuable metal for the chemical reduction ofnitro and azo compounds comparatively expensive, although its use forthis purpose is exceedingly desirable. As a result of my researches andexperiments in this field I have found that tin may be precipitated evenfrom strong acid solutions of tin in hydrochloric acid remaining afterthe reduction of nitro or azo compounds and in the presence ofhigh-current densities if the re ducing process is so conducted that thetin employed is converted only into stannous chlorid and exists insolution as such together with the resultant amins, while, on the onehand, in the electrolysis of solutions of stannic chlorid the currentenergy is almost completely utilized in regenerating the lower chloridof tin, about twenty per cent. of the Work of the current being lost. Inthe recovery of tin from solutions of stannous chlorid, 011 thecontrary, there is, as I have discovered, no loss of current energy. Itis to be noted, moreover, that the double salts of stannic chlorid andthe amins are, as a rule, much less soluble than the stannous chloridsalts. Hence the former are generally precipitated fromthe reducingsolution, so that they must be diluted with considerable quantities ofwater to be put into condition for Such dilution manifestly leadstoawaste of energy by reason of the increase of resistance to thecurrent.

In carrying out my invention the reduction is always carried out byadding to the electrolyte of hydrochloric acid a quantity of tinsuflicient to in surethe formation of stannous chlorid only instead ofstannic chlorid and to leave an excess of tin. After the completion ofthe reducing process the tin is precipitated from the acid solution bypassing a current having a density of eighteen hundred amperes throughthe same. No electrolytic liberation of hydrogen takes place,so that nocurrent energy is Wasted. After suchseparation of tin the electrolyticbath contains only the pure chlorids of the resultant amins, which maybe crystallized out of the solution by well-known methods in those caseswhere it is not preferred to employ the solutions directly.

' I will now describe my invention more in detail with the aid of thefollowing example, disclosing what I consider the preferred method ofcarrying the same into effect.

Reduction of para amz'doazo bcnzolchlorz'cl.2.334 kilogramsamido-azo-benzolchlorid are intimately mixed with 2.66 kilograms ofelectrolytically-precipitated powdered tin. Five kilograms water arethen added and the whole is well mixed, whereupon 4.5 liters of fuminghydrochloric acid are gradually added. After the reduction due to thismixture has been completed the reduction bath or solution is maintainedin a heated condition for several hours and then allowed to 0001. Aftercooling the same is drained from the tin which exists in excess. Thereduction solution is then poured into the cathode-space of anelectrolytic cell whose anode-space is separated from the saidcathode-space by a diaphragm. Any indifferent metal may serve as cathodeand any indifferent conductor will answer as anode. The current employedfor precipitation has a current density of about eighteen hundredamperes; but toward the close of the operation, when the concentrationof the tin ions decreases considerably, it is advantageous andpreferable to reduce this current density. In this manner 2.50 kilogramsof the tin in the form of beautiful oblong crystalline scales or fineplates are recovered from the 2. 66 kilograms originallyemployed. Thisform of tin is Very well adapted to the reduction of nitro and azocompounds and much more soluble than the ordinary granular tin, forexample. The mother-liquor remaining after the recovery of the tin maythen be saturated with hydrochloric-acid gas in the cold, whereby thechlorid of para-phenyl-diamin is precipitated.

In the accompanying drawing I have represented one out of the manypossible forms of apparatus and electrolytic cells for carrying out theprocess involved in my invention.

In the drawing, A represents the anodechamber, containing theanode-electrolyte, and a the anode; O, the cathode-chamber, containingthe cathode-electrolyte, and c the cathode, while cl represents adiaphragm of any suitable material for the separation of the twoelectrolytes according to the usual manner.

S represents a suitable stirrer arranged within the cathode-electrolyte,the spindle or shaft 3 of which may be connected with any suitablesource of power by a belt and pulley B P, as shown, or in any preferredway.

The cooling of the cathode-compartment may be effected by a cooling-coilT, arranged within the said cathode -compartment, as

shown, said coil serving for the circulation of any cooling fluid, suchas cold water.

What I claim, and desire to secure by Letters Patent of the UnitedStates, is-

1. The continuous process of reducing azo compounds which consists inmixing such compoundswith tinand hydrochloric acid in such proportionsthat stannous chlorid is formed, and then electrolytically separatingthe tin from the bath.

2. The continuous process of reducing azo and nitro compounds whichconsists in mixing such compounds with finely-divided tin and water,then adding fuming hydrochloric acid in such proportions that onlystannous chlorid is formed, and then electrolytically separating the tinfrom the bath.

3. The continuous process of reducing azo and nitro compounds whichconsists in mixing such compounds with finely-divided tin and water,then adding fuming hydrochloric acid in such proportions that onlystannous chlorid is formed, then maintaining the whole at an elevatedtemperature for several hours, then cooling, and, finally, draining thesolution from the excess of tin and separating the tin from the bath byelectrolysis.

4. The continuous process of reducing azo compounds which consists inmixing such compounds with tin and hydrochloric acid in 6. Thecontinuous process of reducing azo and nitro compounds which consists inmixing such compounds with finely-divided tin and water, then addingfuming hydrochloric acid in such proportions that only stannous ch loridis formed, then maintaining the whole at an elevated temperature forseveral hours, then cooling then draining the solution from the excessof tin, and thenseparating' the tin from the stannous chlorid by anelectric cur rent of high density.

7. The continuous process of reducing azo and nitro compounds whichconsists in mixing such compounds with tin and hydrochloric acid in suchproportions that stannous chlorid is formed, then subjecting thisreduction-bath in the cathode-space of an electrolytic cell to theaction of an electric current of high densitythrough the same, wherebythe tin is precipitated from the bath, and then employing the tin thusrecovered to repeat the above process.

Ito

S. The continuous process of reducing azo and passing an electriccurrent of high den and nitro compounds which consists in 'miX- sitythrough the same, and then employing the ing such compounds withfinely-divided tin tin thus recovered to repeat the above process.

, and Water, then adding fuming hydrochloric In testimony whereof Iaffix my signature 5 acid in such proportions that only stannous inpresence of two Witnesses.

chlorid is formed, then maintaining the Whole T j 7 at an elevatedtemperature for several hours, MAIL LUOHNER' cooling and fin allydraining the solution from Witnesses: the excess of tin, then pouringthe solution JACOB ADRIAN,

10 into the cathode-space of an electrolytic cell FRITZ ACH.

